Chandra X-ray Image of Abell 2029
This Chandra image is a galaxy cluster from the
latest study of dark energy (from a total of 26 clusters in the
sample). Abell 2029's distance corresponds to a light travel time of 1
billion years. The red diffuse emission shows hot intergalactic gas, heated to about 100 million degrees by the enormous gravity in the cluster, and visible only in X-rays. The distances to the clusters in the sample can be derived from the
Chandra observations by calculating the relative amounts of hot gas and
dark matter. These distances show that the expansion of the Universe
began accelerating about six billion years ago.Scale: Image is 8 x 5 arcmin(Credit: NASA/CXC/IoA/S.Allen et al.)More Information on Abell 2029

Optical Image of Abell 2029
This optical image from the Kitt Peak 0.9m telescope shows Abell 2029, a
cluster of galaxies. A large elliptical galaxy is visible in the center of the image, surrounded by smaller galaxies. This galaxy cluster has a redshift of 0.078, at a distance corresponding to a light travel time of one billion years.Scale: Image is 8 x 5 arcmin(Credit: NOAO/Kitt Peak/J.Uson, D.Dale, S.Boughn, J.Kuhn)

X-ray/Optical Composite of Abell 2029
This optical (blue) and x-ray (red-orange) composite image shows Abell 2029, a cluster of galaxies. A large elliptical galaxy is visible in the center of the image, surrounded by smaller galaxies. The red diffuse emission shows hot intergalactic gas, heated to about 100 million degrees by the enormous gravity in the cluster, and visible only in X-rays. This galaxy cluster has a redshift of 0.078, at a distance corresponding to a light travel time of one billion years.Scale: Image is 8 x 5 arcmin(Credit: Optical: NOAO/Kitt Peak/J.Uson, D.Dale; X-ray: NASA/CXC/IoA/S.Allen et al.)

Chandra X-ray Image of MS2137.3-2353
This Chandra image is a galaxy cluster from the
latest study of dark energy (from a total of 26 clusters in the
sample). MS2137's distance corresponds to a light travel time of 3.6 billion years. The red diffuse emission shows hot intergalactic gas, heated to about 100 million degrees by the enormous gravity in the cluster, and visible only in X-rays. The distances to the clusters in the sample can be derived from the Chandra observations by calculating the relative amounts of hot gas and
dark matter. These distances show that the expansion of the Universe
began accelerating about six billion years ago.Scale: Image is 8 x 5 arcmin(Credit: NASA/CXC/IoA/S.Allen et al.)

Chandra X-ray Image of MACSJ1423.8+2404
The Chandra X-ray image of the galaxy cluster MACSJ1423 shows hot gas displayed in red. The mass of the hot gas is about 6 times greater than the mass of all the billions of stars in all of the galaxies in the cluster. This galaxy cluster has a redshift of 0.54, at a distance corresponding to a light travel time of 5.4 billion years.Scale: Image is 8 x 5 arcmin(Credit: NASA/CXC/IoA/S.Allen et al.)View Animation of MACSJ1423.8+2404

Optical Image of MACSJ1423.8+2404
This image of the galaxy cluster MACSJ1423 is a 3-color optical image from the Subaru prime focus camera. It shows white and blue galaxies centered around a large elliptical galaxy. The mass of the hot gas is about 6 times greater than the mass of all the billions of stars in all of the galaxies in the cluster. This galaxy cluster has a redshift of 0.54, at a distance corresponding to a light travel time of 5.4 billion years.Scale: Image is 2.56 x 1.6 arcmin(Credit: NAOJ/Subaru/H.Ebeling)View Animation of MACSJ1423.8+2404

X-ray/Optical Composite of MACSJ1423.8+2404
This composite image shows views of the galaxy cluster MACSJ1423, using optical and X-ray telescopes. The optical image, a 3-color composite from the Subaru prime focus camera, shows white and blue galaxies centered around a large elliptical galaxy. The Chandra X-ray image shows hot gas displayed in red. The mass of the hot gas is about 6 times greater than the mass of all the billions of stars in all of the galaxies in the cluster. This galaxy cluster have a redshift of 0.54, at a distance corresponding to a light travel time of 5.4 billion years.Scale: Image is 2.56 x 1.6 arcmin(Credit: Optical: NAOJ/Subaru/H. Ebeling; X-Ray: NASA/CXC/IoA/S.Allen et al.)

Chandra X-ray Image of MS1137.5+6625
This Chandra image is a galaxy cluster from the
latest study of dark energy (from a total of 26 clusters in the
sample). MS1137's distance corresponds to a light travel time of 7.9 billion years. The red diffuse emission shows hot intergalactic gas, heated to about 100 million degrees by the enormous gravity in the cluster, and visible only in X-rays. The distances to the clusters in the sample can be derived from the Chandra observations by calculating the relative amounts of hot gas and
dark matter. These distances show that the expansion of the Universe
began accelerating about six billion years ago.Scale: Image is 8 x 5 arcmin(Credit: NASA/CXC/IoA/S.Allen et al.)

X-ray Distance Measurement Technique
This set of illustrations shows the technique used to make distance
measurements to galaxy clusters. Chandra's observations are used to
determine the ratio of the mass of the hot gas and the mass of the dark
matter in different galaxy clusters. This "gas fraction" depends on the
assumed distances to the clusters, which in turn depends on the amount of
matter and dark energy in the Universe. Because galaxy clusters are
extremely large, the gas fraction should be the same for every cluster, and
so the distances to the clusters are adjusted to satisfy this
requirement. Each of these 3 illustration shows Chandra in the top left,
observing a galaxy cluster, shown in the top right (in red). The relative
amounts of hot gas (in red) and dark matter (in blue) are shown at the
bottom, with the green marker giving the expected, correct amount. The
first illustration shows a gas fraction that is too small, implying that
the distance to the cluster is too small, the second shows the correct gas
fraction and distance, and the third illustration shows a gas fraction and
distance that are too large.(Credit: NASA/CXC/M.Weiss)View X-ray Distance Measurement Technique animation

Energy Distribution of the Universe
The new Chandra observations include estimates of the total energy content
of the Universe. As shown in this illustration, dark energy is estimated to
contribute about 75% of the energy in the Universe, dark matter about 21%
and normal matter about 4%. Only the normal matter can be directly detected
with telescopes, and about 85% of this is hot, intergalactic gas, as
detected in Chandra observations of galaxy clusters.(Credit: NASA/CXC/M.Weiss)

Three Possible Futures for the Universe
This illustration shows three possible futures for the Universe, depending
on the behavior of dark energy, by showing how the scale of the Universe
may change with time. If dark energy is constant, as the new Chandra
results suggest, the expansion should continue accelerating forever. If
dark energy increases, the acceleration may happen so quickly that
galaxies, stars, and eventually atoms will be torn apart, in the so-called
Big Rip. Dark energy may also lead to a recollapse of the Universe, in the
Big Crunch. The illustration also shows the early decelerating expansion of
the Universe, followed by the accelerating phase that started about 6
billion years ago.(Credit: NASA/CXC/M.Weiss)

Animation Stills: Effects of Dark Energy
These still images show the expansion history of the Universe by modeling
the Universe as a two-dimensional grid of galaxies. The Big Bang, shown
as a flash of light, is immediately followed by rapid expansion of the
Universe. This expansion then slows down because of the gravitational
attraction of the matter in the Universe. As the Universe expands, the
repulsive effects of dark energy become important, causing the expansion
to accelerate.(Credit: NASA/STScI/G. Bacon)View Animation of the Effects of Dark Energy

Animation Stills: Galaxy Cluster
These still images show a galaxy cluster, the largest gravitationally-bound
objects in the Universe. Individual galaxies are shown in white and
yellow, and the intergalactic gas is shown in red. Galaxy clusters contain
as much mass as a million billion suns. The strong gravitational pull of
this matter squeezes the gas and heats it to about 100 million degrees,
making it only detectable in X-rays. Chandra found direct evidence for
cosmic acceleration and dark energy, based on distance measurements to a
sample of galaxy clusters.(Credit: NASA/CXC/A. Hobart)View Animation of a Galaxy Cluster